How can I override the session ID for a node.js express session (using passport)

I'm implementing a passport strategy that calls our internal auth service. The internal auth service generates the session ID, so I need to make sure the connect session uses that ID instead of the default generated ID.

Is there a way to do this? Is it possible to provide my own hook function to connect to produce the session id? I can't imagine it's as simple as setting session.id or anything like that, because I don't have control over when or how connect actually creates the session.